In the known construction of modern sash frames the frame members, especially the side portions, are usually made from aluminium or plastics and of channel section. A coiled ribbon spring is mounted in each side channel at each side of the window sash and having its tongue operatively connected to the sliding sash frame. Thus, as the window is moved from a closed to an open position the springs are unwound under tension to support the sliding sash frame in any desired open position. Such coiled ribbon springs are compact and simple in operation.
A problem arises where the sliding sash is a heavy one, for example where double-glazed or especially thick glass is used. Because higher rated springs are often more bulky, it has been a practice to utilise multiple spring arrangements with two springs working in unison at each channel location to obtain the desired higher spring rating. In such arrangements, the springs are mounted one above the other; sometimes mounted for rotation in the same directional sense but preferably in opposite senses so that tongues of respective springs can be operatively connected at spaced-apart positions of the sliding sash frame. This arrangement makes for smoother running.
It has been proposed to provide four springs at each location but it is a problem with such multiple spring arrangements that they are difficult to assemble, since a tongue of each spring has to be engaged with the sliding frame element, and if the springs have tongues of the same length then one or more of the springs is under tension during assembly (and also after assembly in all positions of the sliding window sash, i.e. even when the sash is closed). To avoid the latter problem, though not the former, springs with extended tongues (when untensioned) can be used. It is obviously desirable that the number of different types of spring used in a particular construction should be kept to a minimum. There is also a problem that space is at a premium in such channels and the overlapping of tongues of upper springs alongside lower springs increases assembly problems and the likelihood of friction, and jamming. The invention seeks to provide a means of mitigating or obviating such problems.